This unfortunately does not solve your problem since all client side data form submissions are circumventable. If you must use a WYSIWYG ,then what you really need to make sure to do is to cover all your bases on the form's validation and display. You can strip out all script tags and make sure to remove any event attributes and javascript code in links href attributes.

If it is acceptable to only allow a specific subset of tags I would suggest either using BBML, BBCode, or Markdown.

Something to consider is that while stripping the tags out in the browser with TinyMCE is a good idea, it makes a fatal assumption that the user is going to be submitting content via the browser. Anything that you do in the browser needs to be duplicated on the server because attackers can bypass any validation that happens in the browser.